1. Field of Invention
The present invention relates to driving methods and driving circuits for electro-optical devices which perform gray-scale display control using pulse-width modulation, electro-optical devices, and electronic apparatuses.
2. Description of Related Art
Electro-optical devices, such as liquid crystal displays using liquid crystal as electro-optical material, are widely used as display devices in place of cathode-ray tubes (CRTs) in display devices of various information processing apparatuses and in liquid crystal televisions.
By way of example, a conventional electro-optical device has the following structure. Specifically, the conventional electro-optical device includes an element substrate on which pixel electrodes aligned in the form of a matrix and switching devices such as TFTs (Thin Film Transistors) connected to the pixel electrodes are provided, an opposing substrate on which counter electrodes opposed to the pixel electrodes are formed, and liquid crystal, i.e., electro-optical material, filled between the two substrates. With this arrangement, when a scanning signal is supplied to the switching devices via scanning lines, the switching devices become active. In this active state, when an image signal with a voltage in accordance with a gray-scale level is supplied to the pixel electrodes through data lines, a charge in accordance with the voltage of the image signal is accumulated in the liquid crystal layer between the pixel electrodes and the counter electrodes. When the switching devices enter an off state after the charge has been accumulated, the accumulated charge in the liquid crystal layer is maintained by the capacitance of the liquid crystal layer and by storage capacitors. Accordingly, when the switching devices are driven to control the amount of charge accumulated in accordance with the gray-scale level, alignment of the liquid crystal varies according to each pixel, that is, the gray-scale level varies according to each pixel. As a result, gray-scale display can be performed.
It is only necessary to accumulate charge in the liquid crystal layer of each pixel for a partial time period. First, a scanning-line driving circuit sequentially selects each scanning line. Second, a data-line driving circuit sequentially selects each data line within the scanning-line selection time period. Third, an image signal with a voltage in accordance with a gray scale is sampled on the selected data line. As a result, time-division multiplexing driving in which the scanning line and the data line are shared by a plurality of pixels is made possible.